One of the things that often leaves out-of-staters speechless about California is Proposition 65. It's not that a citizens group can sue a company for failing to warn of the presence of a chemical in a product that bothers out-of-staters, it is that there is no agreed safe level above which a warning is required. Prop 65 allows a product seller to forego a warning if there is "no significant risk," but determining whether there is significant risk is an expensive science project. To a single product seller, that science project usually isn't worth the money. The end result is that in deciding whether to place a warning on a product, a seller usually ignores the likely dose, and therefore ignores the true risk. Thus, Proposition 65 encourages companies to place warnings on products that, practically speaking, don't pose a threat to anyone, and that often pose very small or nonexistent risks in relation to the real toxicological risks that people face everyday, such as drugs, smoking, air pollution and workplace exposures to chemicals. There is no prioritization of risks under Proposition 65. Sometimes enforcers go after real risks and sometimes not, and there is no regulatory authority to guide enforcement towards real risks.
The absence of prioritization is becoming clearer now as OEHHA (Office of Environmental Health Hazard Assessment) struggles to deal with acrylamide in foods. Acrylamide is produced in many foods, such as bread and french fries, when they are cooked. The levels present in cooked foods are many times higher than the levels that OEHHA has determined to pose no significant risk. The food industry is pushing to exempt acrylamide in cooked foods from Prop 65's warning requirement on the grounds that the acrylamide is "naturally occurring," while environmentalists are arguing that OEHHA has no authority to create an exemption.
Whoever prevails, the argument just highlights the arbitrariness of Prop 65 warnings. There are no warnings under Prop 65 on naturally occurring carcinogens in peanut butter and many other foods, but there are warnings, when you get into an elevator in California for example, that point out that there is a theoretical risk from chemicals in indoor air. Now we may get a warning that bread is "known to the State of California to cause cancer." It is highly unlikely that a rational regulatory agency would structure enforcement in this manner.